Process for extract-separation of aromatic hydrocarbons

ABSTRACT

A PROCESS FOR EXTRACT-SEPARATING AROMATIC HYDROCARBONS HAVING LARGER BASICITY INTO A HYDROGEN FLUORIDE PHASE BY ALLOWING AN EXTRACTING AGENT CONSISTING OF HYDROGEN FLUORIDE AND BORON TRIFLUORIDE TO COME IN CONTACT WITH A MIXTURE CONTAINING TWO OR MORE AROMATIC HYDROCARBONS HAVING DIFFERENT BASICITY FROM EACH OTHER. MORE PARTICULARLY, A PROCES FOR EXTRACT-SEPARATING AROMATIC HYDROCARBONS IN A   HIGH YIELD AND PURITY WITHOUT SUBSTANTIALLY REFLUXING SAID AROMATIC HYROCARBON HAVING LARGER BASICITY, HERETOFORE CONSIDERED A NECESSITY, BY FEEDING EXTRACTING AGENT CONSISTING OF HF AND BF3, AND DILUENT IN HIGHLY PRECISE AMOUNTS ACCORDING TO A PREDETERMINED CORRELATION.

May 18, 1971 YQSHlRQ rro EI'AL 3,579,599

PROCESS FOR EXTRACT-SEPARATION 0F AROMATIC HYDROCARBONS Filed Nov. 18,1968 3 Sheets-Sheet 1 May 18, 1971 Filed Nov. 18, 1968 3 Sheets-Sheet 2OIO May 18, 1971 Filed Nov. 18, 1968 YOSHIRO ITO PROCESS FOREXTRACT-SEPARATION OF AROMATIC HYDROCARBONS 3 Sheets-Sheet 3 UnitedStates Patent O 3,579,599 PROCESS FOR EXTRACT-SEPARATION OF AROMATICHYDROCARBONS Yoshiro Ito, Tarnotsu Ueno, Takashi Nakano, and KazuoOkamoto, Kurashiki-shi, Japan, assignors to Japan Gas- Chemical Company,Inc., Tokyo, Japan Filed Nov. 18, 1968, Ser. No. 776,728

Claims priority, application Japan, Nov. 21, 1967,

42/ 74,896 Int. Cl. Ctl7c 7/10 Int. Cl. 260674 Claims ABSTRACT OF THEDISCLOSURE A process for extract-separating aromatic hydrocarbons havinglarger basicity into a hydrogen fluoride phase by allowing an extractingagent consisting of hydrogen fluoride and boron trifluoride to come incontact with a mixture containing two or more aromatic hydrocarbonshaving different basicity from each other. More particularly, a processfor extract-separating aromatic hydrocarbons in a high yield and puritywithout substantially refluxing said aromatic hydrocarbon having largerbasicity, heretofore considered a necessity, by feeding extracting agentconsisting of HF and BF and diluent in highly precise amounts accordingto a predetermined correlation.

CROSS-REFERENCE TO RELATED APPLICATIONS This invention is an improvementof a copending application, Ser. No. 555,168 (date of application: June3, 1966). The object of said copending application is given below:

A process for continuously extract-separating m-xylene from a mixture ofxylenes containing m-xylene and at least one xylene isomer (inclusive ofethylbenzene) other than m-xylene comprising the steps of charging saidxylene mixture, reflux m-xylene, diluent, BF, and liquid HF into anm-xylene extractor, and extracting m-xylene in a continuouscountercurrent extraction method, characterized by selectivelyextracting m-xylene from said xylene mixture under such selectedoperating conditions of said extractor as the mole ratio of BF /HF inthe HF extract withdrawn from said m-xylene extractor, that is, theconcentration of xylene, in the hydrocarbon phase at the HF extractwithdrawal section (final stage), and Brn, that is, the mole ratio ofm-xylene/BF in the HF extract, will substantially satisfy the 'y-flmcorrelation on 'y-flm shown by such a diagram as FIGS. 24.

This invention is based on the discovery that separation of aromatichydrocarbons in a high yield and purity is possible without reflux ofm-xylene a step heretofore been considered indispensable.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a process for extract-separating high basicity aromatichydrocarbons into a hydrogen fluoride phase by allowing an extractingagent consisting of hydrogen fluoride and boron trifluoride to contact amixture containing two or more aromatic hydrocarbons having ditferentbasicity from each other.

This invention is applicable to a process for extract separatingm-xylene from C aromatic hydrocarbon fraction; a process forextract-separating mesitylene from C aromatic hydrocarbon fraction; or aprocess for extractseparating aromatic hydrocarbons having a highboiling point from a mixture of xylenes and aromatic hydrocarbons havingthe high boiling point.

For the extract-separation of such aromatic hydrocarbons, this inventionprovides a process for separating Patented May 18, 1971 aromatichydrocarbons in a higher yield and purity than ever before without therefluxing heretofore considered necessary.

When considered from a diiferent viewpoint, this invention is animprovement over the aforementioned process for extract-separatingaromatic hydrocarbons. This improvement eliminates the necessity ofrecovering excessive diluent and installing auxiliary equipment relatedto the reflux, and, accordingly, increases the capacity of theextracting system and reduces utility requirements, for its operation.

DESCRIPTION OF THE PRIOR ART There have been numerous experimentsconducted to selectively extract a constituent of aromatic hydrocarbonsby employing BF -HF extracting agent, and those considered most closelyrelated to this invention are US. Pat. 2,521,444, US. Pat. 2,727,078,and US. Pat. 2,848,- 518. Although US. Pat. 2,521,444 (Brooke et a1.)relates to a process for separating an isomeric mixture of lowerdialkylbenzenes by employing BF -HF extracting agent, a number ofextractors are utilized connected in series and into each of them BF -HFextracting agent is fed. This process is, however, considered primitive.US. Pat. 2,727,- 078 (Shoemaker) relates to a process for separatingmxylene from an isomeric mixture of xylenes by employing BF -HFextracting agent, however, the characteristic of this process lies informing a complex mixture of mxylene and at least one xylene isomerother than m-xylene, with BF in HF to which m-xylene and diluent areadded, thereby selectively decomposing complex mixtures of otherisomers, leaving m-xylene as the only complex form. It is to be notedthat in this process addition of m-xylene is an absolutely necessaryfactor. US. Pat. 2,848,518 (Fragen) describes the total system relatedto a process for separating each constituent from a mixture of xylenesbut description of said extraction process is extremely simple andcovers no more than what is already described hereabove.

SUMMARY OF THE INVENTION Accordingly, this invention relates to aprocess for extract-separating high basicity aromatic hydrocarbons intoa hydrogen fluoride phase by allowing an extracting agent consisting ofhydrogen fluoride and boron trifluoride to contact with a mixturecontaining two or more aromatic hydrocarbons having different basicityfrom each other, characterized by extract-separation of aromatichydrocarbons without substantially refluxing aromatic hydrocarbons to beextracted. Furthermore, this invention, employing as raw material Caromatic hydrocarbon fraction (referred to as C fraction hereinafter)containing m-xylene and at least one, xylene isomer other than mxylene,and feeding said C fraction, diluent, BF and liquid HF to an m-xyleneextractor, relates to a process for extract-separating m-xylene in acontinuous countercurrent extraction, characterized by continuousextractseparation of m-xylene from said C fraction containing m-xyleneand at least one xylene isomer other than mxylene without substantiallyrefluxing m-xylene under such operating conditions of said extractor asthe mole ratio of BF HF in the HF extract withdrawn from said m-xyleneextractor, 'y, that is, the concentration of xylene in the hydrocarbonphase at the HF extract withdrawal section (final stage), and pm, thatis, the mole ratio of total mxylene/BF in the HF extract, willsubstantially satisfy the correlation shown by such a 'y-flm correlationdiagram as FIGS. 24.

DEFINITION OF THE TERMS To define the terms used in this invention, theterm C aromatic hydrocarbon fraction referred to in the specificationmeans C aromatic hydrocarbon fraction obtained by separating from apetroleum constituent containing aromatic hydrocarbons, Which wasobtained by catalytic reforming, thermal cracking of petroleum or from atar constituent containing aromatic hydrocarbons, normally containsm-xylene, o-xylcne, p-xylene and ethylbenzene as principal constituentsand a small amount of benzene, toluene, etc.

Also, the term xylene isomers other than m-xylene includes ethylbenzenein addition to o-xylene and pxylene.

The term raflinate means a hydrocarbon phase remaining without beingextracted into the HF phase in the extractor, and when extractingm-xylene from C aromatic hydrocarbon fraction, it means a mixture of Caromatic hydrocarbon substantially not containing m-xylene, diluentadded in the course of extracting mxylene, a very small amount of HF, BFbenzene, toluene, etc. Accordingly, the diluent, a very small amount ofHF, BF etc. are removed through distillation of the raflinate, andresidual C aromatic hydrocarbon fraction is obtained.

The term extract product means aromatic hydrocarbons to be extracted inthe HF extract. The term extrac means the sum of extracting agent andextract product.

BRIEF DESCRIPTION OF THE DRAl/VINGS FIG. 1 is a highly simplified flowsheet to illustrate the principle of extraction. FIG. 2 shows the -fimat temperature C. as BF HF in parameter between m, signifyingcorrelation the mole ratio of m-xylene/B'F in the HF extract and y,signifying the concentration of xylene in the hydrocarbon phase at theHF extract withdrawal section (final stage). FIG. 3 illustrates the samerelation shown in FIG. 2 at C., and FIG. 4 also illustrates the samerelation shown in FIG. 2 at +15 C.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention provides anefiective process for selectively extracting a certain specifichydrocarbon from a mixture of more than two aromatic hydrocarbons havingdiflerent basicity from each other. The process is also effective forextract-separating mesitylene from a mixture current extracting system1, and at the same time, hydrogen fluoride and boron trifluoride are fedthrough pipe 3 and pipe 4 respectively to the top of the extractor 1,and countercurrent contact of the HF-BF phase and C fraction phase isallowed to take place in the extractor. In this instance, diluent is fedinto the extractor 1 through pipe 5 to improve its selectivity, andfurthermore, a portion of extract-separated high purity m-xylene is fedback as reflux to the extractor 1 through pipe 6. The extract andrafiinate are withdrawn from the extractor 1 through pipe 8 and pipe 7,respectively. Above process has been considered normal with the priorart. The inventors have already discovered that in order to extract intothe HF extract the sum of the m-xylene in the feed C fraction and refluxm-xylene, that is, the entire amount of m-xylene to be fed into them-xylene extractor, without substantially leaving any residual m-xylenein the raflinate, it is necessary to feed HF, BF diluent, and extractproduct in such a proportion as will substantially satisfy a highlyprecise correlation, that is, the correlation shown in FIGS. 24 (Ser.No. 555,168).

The inventors have advanced further with the study to extract-separatem-xylene from the C fraction, utilizing such correlation as mentionedabove, and as a result, discovered an unexpected fact that the reflux ofm-xylene, heretofore considered as absolutely necessary in theextract-separation of high purity m-xylene, is not always necessary, andon the basis of this discovery have developed this invention.

Namely, in the process heretofore employed, the amount of reflux is at areflux ratio of 0.54, while in this invention without substantiallyrefluxing means a reflux ratio of 0.2 or less (including 0.0). Thereflux ratio is a value meaning the value of said amount of refluxdivided by the value of the total amount of extract product in the HFextract withdrawn from the extractor minus the amount of reflux to befed back to the extractor as reflux.

Next, Table 1 shows the result of measurement of mxylene/BF mole ratioin the HF extract in both cases using pure m-xylene only and using purem-xylene and a known quantity of diluent added to the system. Asdiluent, n-hexane is employed and the measured temperature is 0 C.

TABLE 1 m-Xylene m-Xylene nrXylene in m-Xylene in HF in hydrohydrocarbonFeed, Feed, BF ab- BF lfeed dissolved (mole) carbon phase/total m-xylenen-hexane Feed, HF sorbed in Parameter. m-xylene in HF BE in HF phasehydrocar- No. (mole) (mole) (mole) HF (mole) BFs/HF (mole) (mole) (mole)Bin (mole) bon I L 290 3. 0. 099 0. 0288 0. 077 0. 129 1. 30 0. 217 0.0628 0. 168 0. 434 2. 00 0. 311 0. 0903 0. 241 0. 672 2. l6 0. 496 0.1440 0. 385 1. 20 2. 41 0. 546 0. 1580 0. 425 1. 29 2. 3

2- 0. 942 0. 233 3. 40 0. 294 O. 0864 0. 312 0. 503 I. 71 O. 439 0. 6530. 469 0. 1380 0. 498 0. 727 1. 0. 125 0. 480 0. 682 0. 2003 0. 723 0.790 1. 16 0. 152 0. 395

3 0. 658 0. 349 3. 4O 0. 145 0. 0426 0. 220 O. 172 1. 19 0. 486 0. 5830. 294 0. 0865 0. 447 0. 399 l. 36 0. 259 O. 426 0. 415 0. 1221 0. 6320. 518 1. 25 0. 140 0. 286 0. 586 0. 1725 0. 892 0. 580 0. 99 0. 078 0.183

of C aromatic hydrocarbons, or for extract-separating a Here n and 'yare defined by the following formula: hydrocarbon having a high boilingpoint from a mixture to l a i v of xylene and aromatic hydrocarbonshavmg said higher [3 3mm t c hydmfiarbons m HF extract (mole) boilingpoint. However, this invention is particularly ef fective in providingan industrial process for extractseparating m-xylene from the Cfraction.

Accordingly, in the following general explanation, extract-separation ofm-xylene from the C fraction is given as an example for simplifying theexplanation and for easier understanding.

Referring to FIG. 1, the raw material C fraction is fed through pipe 2into the center of the continuous counter- BE, in HF extract (mole)(flm: 5 in case where aromatic hydrocarbon is pure m-xylene) aromatichydrocarbons in hydrocarbon phase 1: in equilibrium relation with HFextract (mole) aromatic hydrocarbons in hydrocarbon phase in equilibriumrelation with HF extract (mole) diluent in hydrocarbon phase (mole)Also. the hydrocarbon phase means residual hydrocarbons not extracted inthe HF extract phase (solution of aromatic hydrocarbons and diluent).FIGS. 2-4 show the relation obtained from the result related to m-xyleneas the mole ratio of BF /HF in the HF extract as parameter between rim,that is, the mole ratio of m-xylene/BF in the HF extract and 7, that is,the concentration of C aromatic hydrocarbons in the hydrocarbon phase inequilibrium relation with the HF extract. FIG. 2, FIG. 3, and FIG. 4show the value when the measured temperature is C., 20 C. and C.,respectively. In other words, notwithstanding a change in temperatureand diluent employed, the result showing the same tendency isobtainable. Furthermore, according to an experiment as above todetermine dissolved amount of the C fraction containing differentconcentrations of m-xylene, [3 and 8m are substantially equal as long asthe concentration of m-xylene in the HF extract (based on C aromatichydrocarbon) is 94 mole percent or more. The diluent is substantiallypresent in the C aromatic hydrocarbon phase and acts as diluent to the Caromatic hydrocarbon. As is clear from FIGS. 2-4, in case of m-xylene,,Bm, that is, the mole ratio of m-xylene/BF in the HF extract, shows avalue siginficantly deviated from 1 depending on the BF /HF mole ratioin the HF extract, and 'y, that is, the concentration of the aromatichydrocarbons in the hydrocarbon phase.

The -Bm correlation such as those shown in FIGS. 2-4 is particularlyimportant for selective extraction of m-xylene from the C fraction.Namely, in order to selectively extract m-xylene present in the Cfraction as a high purity m-xylene complex, and simultaneously leavesubstantially no m-xylene in the rafiinate, it is necessary to selectthe addition amount of HF and BE; (or, for example, the mole ratio of BF/HF and the amount of BF so as to allow the total m-xylene fed into them-xylene extractor to be extracted in the withdrawn HF extract. Toobtain high purity m-xylene and residual C fraction consistingsubstantially of xylene isomers other than m-xylene, these ratios mustbe determined highly precisely.

In this invention, as the operating conditions of said m-xyleneextractor, the BP /HF mole ratio of the with drawn HF extract must befirst established within the range of 0.02-0.20, followed bydetermination of that is, the concentration of the aromatic hydrocarbonin the hydrocarbon phase at the HF extract withdrawal section (finalstage). Should the BF /HF mole ratio be too low, the amount of needed HFwould increase, hence increased amount of the extract subject todecomposition and increased heat load caused by the decomposition. Also,when the BF /HF mole ratio is increased, the pressure inthe' extractorwill increase. For this reason, selection of the aforementioned range isdesirable. The value of 'y is approximately 0.3 or less. Especiallyit-is known from our experience that when the reflux ratio is zero, thevalue of y becomes to 0.1 or less. Once these ratios are determined,fim, that is, the m-xylene/BF mole ratio in the HF extract, will bedecided to substantially satisfy such 'y-fim equilibrium correlation asshown in FIGS. 2-4, and from value, this determined is the amount of BFto be charged into said m-xylene extractor. The amount of HP to be addedcan be easily determined from the aforementioned selected value of theaddition amount of BF and from the aforementioned selected value of theBF /HF mole ratio in the HF extract.

In this invention, when the amount of reflux is decreased, the ratio ofthe diluent to be fed against the extract product withdrawn from theextract Withdrawal section wil be inevitably increased. This is definedas D by the following formula:

amount of diluent to be fed into extractor (mole) D varies somewhatdepending upon the concentration of the extract product in the rawmaterial; however, when there is absolutely no reflux (that is to saywhen the reflux ratio is zero), D is appropriate in the range of 0.7-10with a 1-5 range being most desirable. When the reflux ratio is 0.2, Dmay be 0.5 or above.

The diluent is removed as raflinate. Stable substances that do notsubstantially dissolve in extracting agent but form a uniform phase withratfinate can be used as diluent, for example, aliphatic saturatedhydrocarbons such as propane, n-butane, i-butane, n-pentane, andn-hexane; alicyclic saturated hydrocarbons such as cyclopentane, andcyclohexane; or halogenated hydrocarbons such as carbon tetrachloride.When carbon tetrachloride is used, the top and bottom positions of theraffinate and the extract are normally reversed. An extractiontemperature of -20-+30 C. and pressure of 1-20 kg./cm. g. are used inthe extractor. The amount of hydrogen fluoride to be fed is 1.8-25 moleagainst one mole of the raw material aromatic hydrocarbon, while theabount of boron trifluoride is about 0.7-1.5 moles against one mole ofthe extract product in the raw material aromatic hydrocarbon. It isdesirable to select the mole ratio of boron trifluoride/ hydrogenfluoride within the range of 002-020. The types of extracting towersuitable for use include such as a packed tower, perforated plate tower,perforated plate pulse tower, extractor equipped with stirrer, and mixersettler.

As mentioned above according to this invention, high basicity aromatichydrocarbons of high purity can be extract-separated in an extremelyhigh yield without substantially refluxing the extract product. As thisinvention does not require reflux of the extract product, the amount ofextract product at the extract withdrawal section is de creased, therebydecreasing the amount of feed diluent. As mentioned earlier, thisdecreases need for recovering excessive diluent and for installing theauxiliary equipment needed in connection with the reflux, nor will therebe any substantial increase in the theoretical number of platesnecessary for extraction, and significant benefits such as increasedcapacity of the extractor are obtained.

EXAMPLE 1 Extracting agent Substance supplied HF 2 BF;

Benzene Toluene Raw material Diluent Exsupplied supplied tract;

Raninate o-Xylene Total of aromatic hydrocarbons n-H exane 297 3No'rE.Unit=mole/hour.

The theoretical number of plates of the extraction tower was 7.5.

REFERENCE EXAMPLE 1 When 39 (mole/hour) of m-xylene (98%) (reflux ratio:0.2) is fed into the extract withdrawal section, using the same amountof diluent as used in Example 1, the theoretical number of plates is 6.7and the mole ratio of boron trifluoride/raw material will also beincreased by 3%, while the extracting capacity of said equipment will bedecreased by 4%, hence, there is practically no difference betweenExample 1 and Reference Example 1. On the other hand, when the amount ofreflux is set at 97 (mole;/hour) (reflux ratio: 0.5), the theoreticalnumber of plates is 6.6 and the mole ratio of boron trifluoride/rawmaterial will increase by 14%. In this instance, an increase in theamount of heat necessary for the recovery of the diluent and cooling ofthe reflux m-xylene is 50 times or more of the amount of heat requiredto cool the C fraction and n-hexane to 5 C. from room temperature anenormous increase in utility requirements. Also, the extraction capacitywill be decreased by 15%. Furthermore, with the reflux m-xylene (refluxratio: 1.0) being set at 194 (mole/hour), the theoretical number ofplates remains practically unchanged at 6.6, While the borontrifiuoride/raw material mole ratio goes up by about 20% with theextraction capacity reduced by about 30%, necessitating still moreutilities.

EXAMPLE 2 Using the same equipment as described in Example 1, the rawmaterial C fraction containing 35%of m-xylene is fed to conductcountercurrent extraction under normal pressure and at +5 C. The resultsobtained are as shown in the following table. As diluent, n-pentane isemployed without reflux.

EXAMPLE 3 The raw material C -C fraction containing 20% of1,3,5-trimethyl benzene was fed so as to allow countercurrent contact totake place under normal pressure and at 8 C., all other conditions beingidentical with those described in Example 1. The results obtained are asfollows Extracting Raw agent material Diluent Ex- Rath- Substancesupplied supplied supplied tract nate HF 691 2 B F 61 1 Ethyl benzene 06 p-Xylene 0. 1 45 m-Xylene- 11 125 o-igene. It i. .1 0. 2 4O 1 ime bsnzenefli 56.7 0. 2

Total of aromatic hydrocarbons 284 68 215 n-Hex ane 227 225 NOTE.Unit=mole/hour.

We claim:

1. A process for continuous countercurrent extractseparation of aromatichydrocarbons into a hydrogen fluoride phase, comprising:

contacting a mixture of two or more aromatic hydrocarbons havingdiiferent basicity from each other with an extracting agent consistingof hydrogen fluoride and boron trifiuoride at a temperature of fromabout 20 C. to +30 C., and

maintaining a reflux ratio up to 0.2.

2. The process of claim 1 wherein extraction is conducted with a BF/I-IF molar ratio of the HF extract of from 0.02 to 0.20, theconcentration 7 of aromatic hydrocarbons in the hydrocarbon phase at theHF extract withdrawal section of the extractor employed has a value ofless than 0.3, and the mole ratio B of the total m-Xylene/BF extract inthe HF extract, will substantially satisfy a curve represented by the -5correlation given in FIG. 2, wherein BF HF is the parameter.

3. The process of claim 1 wherein extraction is conducted with a BF /HFmolar ratio of the HF extract of from 0.02 to 0.20, the concentration 7of aromatic hydrocarbons in the hydrocarbon phase at the HF extractwithdrawal section of the extractor employed has a value of less than0.3, and the mole ratio B of the total mxylene/BF extract in the HFextract, will substantially satisfy a curve represented by the -5correlation given in FIG. 3, wherein BF /HF is the parameter.

4. The process of claim 1 wherein extraction is con-. ducted with a BF/HF molar ratio of the HF extract of from 0.02 to 0.20, theconcentration 7 of aromatic hydrocarbons in the hydrocarbon phase at theHF extract withdrawal section of the extractor employed has a value ofless than 0.3, and the mole ratio B of the total mxylene/BF extract inthe HF extract, will substantially satisfy a curve represented by the7-13 correlation given in FIG. 4, wherein BF /HF is the parameter.

5. The process of claim 1, wherein the aromatic hydrocarbon mixturecomprises a mixture of C aromatic hydrocarbons.

6. The process of claim 5, wherein the aromatic hydrocarbon mixturecomprises a mixture of C aromatic hydrocarbons and the extract productis substantially m-xylene.

7. The process of claim 1, wherein the BF /HF mole ratio is from 0.02 to0.20.

8. The process of claim 1, wherein the molar ratio of HF charge to thearomatic hydrocarbon mixture is from 1.8 to 25.

9. The process of claim 1, wherein the molar ratio of BF /extractproduct is from 0.7 to 1.5.

10. The process of claim 1, wherein the aromatic hydrocarbon mixturecomprises a C aromatic hydrocarbon mixture,

the extract product is substantially 1,3,5-trimethylbenzene, the molarratio of BF-,/ HF is from 0.02 to 0.20, the molar ratio of HF charge tothe aromatic hydrocarbon mixture is from 1.8 to 25,

the molar ratio of BF;,/ extract product is from 0.7 to

1.5, and

the molar ratio of a diluent charge to the extract product is from 0.5to 10.

References Cited UNITED STATES PATENTS 2,532,276 12/1950 Birch et a1.2,848,518 8/1958 Fragen.

CURTIS R. DAVIS, Primary Examiner UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3 579 599 Dated y 18 a 1971 YoshiroIto et a1.

Inventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 4, Table 1, under the heading "In-Xylene in hydrocarbon phase(mole) and referring to No. 2, "0.125" should read 0.215 Column 7, line5, "(mole;/hour)" should read (mo1e; hour) Signed and sealed this 25thday of April 1972.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of PatentsAttesting Officer

